1. Field of the Invention
The present invention relates to an electrical connector, and particularly to a high density, shielded backplane connector used to connect daughter boards with a mother board and transmit high speed signals therebetween.
2. Description of Prior Art
Many electronic systems employ electrical connectors to interconnect printed circuit boards used therewith. It is generally easier and more cost effective to manufacture a system on several printed circuit boards which are then joined together by electrical connectors. A traditional arrangement for joining several printed circuit boards is to have one printed circuit board serve as a backplane. Other printed circuit boards, called daughter boards, are connected to the backplane. Since electronic systems have gotten smaller and faster in handling much more data than ever, electrical connectors must carry more and faster data signals in a smaller space without degrading the signals. High density, high speed electrical connectors, just as their names imply, carrying more and faster data signals in a smaller space through signal contacts are coming into use. As the signal contacts are placed closer and the speed of the signals increases, electromagnetic interference and the cross-talk become an important issue.
U.S. Pat. Nos. 5,066,236 and 5,104,341, both issued to AMP Incorporated, disclose a backplane receptacle connector mountable to a printed circuit board having shield members. Cross-talk shield members are insertable into the rear of the connector housing to shield adjacent rows of terminals from cross-talk, while upper and lower shield members are insertable over the assembly to shield the assembly from EMI/RFI. However, it should be noted that a header for mating with the backplane receptacle connector is provided with grounding contacts to electrically connect with resilient fingers of the upper and lower shield members thereby establishing a grounding circuitry therebetween. The arrangement of positioning the grounding contacts between signal pins of the header reduces the effective signal density of the header. Significantly, the employment of the upper and lower shield members complexes the manufacture of the connector as well as the assembly thereof.
Similar shield member design is implemented in Molex Incorporated product, named MZP(trademark) hard metric connector, which can be found in website of Molex, http://www.molex.com.
U.S. Pat. No. 5,433,617, issued to Framatome Connectors International, dated Jul. 18, 1995, discloses a backplane connector assembly. The backplane connector assembly is composed of a header connector and a receptacle connector, mounted on respective printed circuit boards, wherein the header connector provides first shielding plates therewith while the receptacle connector provides side-by-side positioned, ground contact plates and a second shielding plate therewith. Consequentially, electrical contacts and mechanical supports are established between corresponding parts of the first shielding plate, the second shielding plate and the ground contact plates. Specially, in the coupled position of the assembly, the first shielding plates of the header provides contact springs simultaneously engaging the edges of the ground contact plates and the second shielding plate of the receptacle. Further, the first shield plates and the ground contact plates have individual contact area or contact elements thereof contacting suitable conductor of the printed circuit boards on which the header and the receptacle are respectively mounted. Similarly, the second shielding plate of the receptacle provides contact parts inserted into openings of the corresponding printed circuit board and contacting a corresponding conductor of the printed circuit board. Thus, the ground route of the assembly is formed. Moreover, in an alternative embodiment of the patent, a third shield plate is even provided. Obviously, the connector assembly as described above, is unsuitable for mass-produce due to complicated manufacturing process and assembling process, both of which increase the cost.
In U.S. Pat. No. 6,299,484, which is another patent assigned to Framatome Connectors International, a backplane connector is introduced. The backplane connector comprises at least one shielding plate arranged between two adjacent rows of contact elements, and a shielding member mounted on the assembled connector housings. The shielding member includes a plurality of contact springs stamped therefrom and contacting edges of the shielding plates to achieve a shielding purpose. However, the shielding effectiveness of the patent is not totally satisfied for that the contact between the shielding member and the slender edges of the shielding plates is unreliable.
Hence, an improved backplane connector is desired to overcome the disadvantages of the prior arts.
Accordingly, an object of the present invention is to provide a high speed, high density backplane connector having a shield member to achieve a better EMI protection.
In order to achieve the above-mentioned object, a backplane connector in accordance with the present invention includes a plurality of wafers defining therebetween receiving openings, circuit boards retained in the receiving openings of the wafers, and a shield member covering the wafers and the printed circuit boards. Each wafer includes a dielectric base, a plurality of signal terminals received in one side of the base, and a grounding bus attached on an opposite side of the dielectric base. Each circuit board is provided with signal traces and conductive layer coated thereon. The shield is stamped from a piece of metal sheet and has a horizontally extended intermediate portion and a downwardly extended rear portion. The intermediate portion substantially covers a top of the circuit boards, and the rear portion substantially covers a rear of the circuit boards. A number of resilient tabs are stamped from the intermediate portion and arranged in two staggered rows. Each of the resilient tabs protrudes inwardly and extends between adjacent two circuit boards. The resilient tabs separates adjacent circuit boards and electrically contact with the grounding layers of corresponding circuit boards thereby achieving grounding requirement.